The present invention relates, in general, to the field of Enterprise System Connection (ESCON.TM. is a trademark of International Business Machines Corporation, "IBM") switches. More particularly, the present invention relates to a method and apparatus for the establishment of dynamic ESCON connections from Fibre Channel frames.
A typical ESCON switch is described in U.S. Pat. No. 5,107,489 issued Apr. 21, 1992 for "Switch and its Protocol for Making Dynamic Connections", the disclosure of which is herein specifically incorporated by this reference. Among the switches which are commercially available are the IBM ESCON Director Models 3, 4 and 5 developed in conjunction with McDATA Corporation, Broomfield, Colorado, assignee of the present invention. An ESCON connection has a bandwidth of 20 Mbytes/sec. in a half duplex mode of operation.
On the other hand, Fibre Channel is an integrated set of standards adopted by the American National Standards Institute ("ANSI") which defines protocols for information transfer. The Fibre Channel has a bandwidth of approximately 200 Mbytes/sec. (212 Mbytes/sec.) in full duplex mode of operation (i.e. 106 Mbytes/sec. in each of transmit and receive modes of operation). Information transfer occurs in indivisible units called "frames". Fibre Channel devices are called "nodes", each of which has at least one "port" for access to other ports of other nodes. Currently, fibre channel includes five defined functional levels:
FC-0 defines the physical portions inclusive of media types, connectors and the electrical and optical characteristics needed to connect ports.
FC-1 defines the transmission protocol, including the encoding, order of word transmission and error detection;
FC-2 defines the signaling and framing protocol inclusive of frame layout, frame header content and rules for use;
FC-3 defines common services that may be available across multiple ports in a node; and
FC-4 defines the mapping between the lower levels of Fibre Channel and the command sets that use it, inclusive of the Small Computer System Interface ("SCSI"), Intelligent Peripheral Interface ("IPI"), High Performance Parallel Interface ("HIPPI") and the like.
As previously mentioned, the standard ESCON connection has a bandwidth of 20 Mbytes/second and is half-duplex in operation (i.e. either a "read" or "write" command can be active at one time) while Fibre Channel can provide up to 212 Mbytes/second (106 Mbytes/second in both transmit and receive) at full duplex. It would, therefore, be highly desirable to be able to multiplex multiple ESCON channels over a single Fibre Channel connection to take advantage of the latter's much higher relative bandwidth.